Threaded spinal implant

ABSTRACT

An artificial spinal implant is disclosed which when place between two adjacent vertebrae directly participates and is incorporated in the insuing fusion. Instrumentation and procedure is also disclosed.

This application is a continuation of application Ser. No. 08/480,684,filed Jun. 7, 1995, which is a divisional application of applicationSer. No. 07/968,240, filed Oct. 29, 1992, now U.S. Pat. No. 5,741,253,which is a continuation of application Ser. No. 07/698,674, filed May10, 1991, abandoned, which is a divisional of application Ser. No.07/205,935, filed Jun. 13, 1988, now U.S. Pat. No. 5,015,247.

BACKGROUND

The present invention relates to an artificial fusion implant to beplaced into the intervertebral space left after the removal of a damagesspinal disc.

The purpose of the present invention is to provide an implant to beplaced within the intervertebral disc space and provide for thepermanent elimination of all motion at that location. To do so, thedevice is space occupying within the disc space, rigid, self-stabilizingto resist dislodgement, stabilizing to the adjacent spinal vertebrae toeliminate local motion, and able to intrinsically participate in avertebra to vertebrae bony fusion so as to assure the permanency of theresult.

At present, following the removal of a damaged disc, either bone ornothing is placed into the space left. Placing nothing in the spaceallows the space to collapse which may result in damage to the nerves;or the space may fill with scar tissue and eventually lead to areherniation. The use of bone is less than optimal in that the boneobtained from the patient requires additional surgery and is of limitedavailability in its most useful form, and if obtained elsewhere, lacksliving bone cells, carries a significant risk of infection, and is alsolimited in supply as it is usually obtained from accident victims.Furthermore, regardless of the source of the bone, it is only marginalstructurally and lacks a means to either stabilize itself againstdislodgement, or to stabilize the adjacent vertebrae.

A review of related prior art will demonstrate the novelty of thepresent invention.

There have been an extensive number of attempts to develop an acceptabledisc prothesis (an artificial disc). Such devices by design would beused to replace a damaged disc and seek to restore the height of theinterspace and to restore the normal motion of the spinal joint. No suchdevice has been found that is medically acceptable. This group ofprosthetic or artificial disc replacements, seeking to preserve spinalmotion and so are different from the present invention, would include:

U.S. Pat. No. 3,867,728 STUBSTAD—describing a flexible disc implant.

U.S. Pat. No. 4,349,921 KUNTZ—describing a flexible disc replacementwith file like surface projections to discourage device dislocation.

U.S. Pat. No. 4,309,777 PATIL—describing a motion preserving implantwith spiked outer surfaces to resist dislocation and containing a seriesof springs to urge the vertebrae away from each other.

U.S. Pat. No. 3,875,595 FRONING—describing a motion preserving bladderlike disc replacement with two opposed stud-like projections to riskdislocation.

U.S. Pat. No. 2,372,622 FASSIO (FRENCH)—describing a motion preservingimplant comprising complimentary opposed convex and concave surfaces.

In summary then, these devices resemble the present invention only inthat they are placed within the intervertebral space following theremoval of a damaged disc. In that they seek to preserve spinal motion,they are diametrically different from the present invention which seeksto permanently eliminate all motion at the spinal segment.

A second related area of prior art includes those devices utilized toreplace essentially wholly removed vertebra. Such removal is generallynecessitated by extensive vertebral fractures, or tumors, and is notassociated with the treatment of disc disease. While the presentinvention is to be placed within the disc space, these other vertebraldevices cannot be placed within the disc space as at least one vertebrahas already been removed such that there no longer remains a “discspace.” Furthermore, these devices are limited in that they seek toperform as temporary structural members mechanically replacing theremoved vertebra (not a removed disc), and do not intrinsicallyparticipate in supplying osteogenic material to achieve cross vertebraebony fusion. Therefore, again unlike the present invention whichprovides for a source of osteogenesis, use of this group of devices mustbe accompanied by a further surgery consisting of a bone fusionprocedure utilizing conventional technique. This group consisting ofvertebral struts rather than disc replacement would include thefollowing:

U.S. Pat. No. 4,553,273 WU—describing a turnbuckle like vertebral strut.

U.S. Pat. No. 4,401,112 REZAIAN—describing a turnbuckle like vertebralstrut with the addition of a long stabilizing staple that spans themissing vertebral body.

U.S. Pat. No. 4,554,914 KAPP—describing a large distractible spike thatelongates with a screw mechanism to span the gap left by the removal ofa entire vertebra and to serve as an anchor for acrylic cement which isthen used to replace the missing bone (vertebra).

U.S. Pat. No. 4,636,217 OGILVIE—describing a vertebral strut mechanismthat can be implanted after at least one vertebra has been removed andwhich device consists of a mechanism for causing the engagement ofscrews into the vertebra above and the vertebra below the one removed.

In summary then, this group of devices differs from the presentinvention in that they are vertebra replacements struts, do notintrinsically participate in the bony fusion, can only be inserted inthe limited circumstances where an entire vertebra has been removed fromthe anterior approach, and are not designed for, or intended to be usedfor the treatment of disc disease.

A third area of prior art related to the present invention includes alldevices designed to be applied to one of the surfaces of the spine. Suchdevices include all types of plates, struts, and rods which are attachedby hooks, wires and screws. These devices differ significantly from thepresent invention in that they are not inserted within the disc space,and furthermore do not intrinsically participate in supplying osteogenicmaterial for the fusion.

Therefore, with these devices where permanent spinal immobilization isdesired an additional surgery consisting of a spinal fusion performed byconventional means or the use of supplemental methylmethacrylate cementis required. Such devices applied to the spine, but not within the discspace, would include the following:

U.S. Pat. No. 4,604,995 —STEPHENS—describing a “U” shaped metal rodattached to the posterior elements of the spine with wires to stabilizethe spine over a large number of segments.

U.S. Pat. No. 2,677,369 —KNOWLES—describing a metal column device to beplaced posteriorly along the lumbar spine to be held in position by itsshape alone and to block pressure across the posterior portions of thespinal column by locking the spine in full flexion thereby shifting themaximum weight back onto the patient's own disc.

Other devices are simply variations on the use of rods (e.g. HarringtonLuque, Cotrel-Dubosset, Zielke), wires or cables (Dwyer), plates anscrews (Steffee), or struts (Dunn, Knowles).

In summary, none of these devices are designed or can be used within thedisc space, do not replace a damaged disc, and do not intrinsicallyparticipate in the generation of a bony fusion.

Another area of related prior art to be considered is that of devicesdesigned to be placed within the vertebral interspace following theremoval of a damaged disc, and seeking to eliminate further motion atthe location.

A device is contained in U.S. Pat. No. 4,501,269 BAGBY—describing animplantable device and limited instrumentation. The method employed isas follows: a hole is bored transversely across the joint and then ahollow metal basket of larger diameter than the hole is then poundedinto the hole and then filled with the bone debris generated by thedrilling.

While the present invention (device, instrumentation, and method) mayappear to bear some superficial resemblance to the BAGBY invention, itis minimal, while the differences are many fold and highly significant.These difference include the following:

1. Safety

The present invention provides for a system of completely guardedinstrumentation so that all contiguous vital structures (e.g. largeblood vessels, neural structures) are absolutely protected. Saidinstrumentation also make overpenetration by the drill impossible. Suchover penetration in the cervical spine, for example, would result in thetotal paralysis or death of a patient. In the thoracic spine, the resultwould be complete paraplegia. In the lumbar spine, the result would beparaplegia or a life-threatening perforation of the aorta, vena cava, oriliac vessels. The present invention is atraumatically screwed intoplace while the BAGBY device, in contradistinction, is pounded intoposition. BAGBY describes that the implant is significantly large insize than the hole drilled and must be pounded in. This is extremelydangerous and the pounding occurs directly over the spinal cord which isprecariously vulnerable to percussive injury. Furthermore, while it ispossible for example in the lumbar spine, to insert the presentinvention away from the spinal cord and nerves, the BAGBY device mustalways be pounded directly towards the spinal cord.

Furthermore, since the BAGBY device is pounded into a smooth hole undergreat resistance, and lacking any specific sign feature to secure it,the device is highly susceptible to forceful ejection which would resultin great danger to the patient and a clinical failure. The presentinvention, in contradistinction, is securely screwed into place, andpossesses highly specialized locking threads to make accidentaldislodgement impossible. Because of the proximity of the spinal cord,spinal nerves, and blood vessels, any implant dislodgement as mightoccur with the BAGBY device might have catastrophic consequences.

2. Broad applicability

The BAGBY device can only be inserted from the front of the vertebralcolumn, however, the present invention can be utilized in the cervical,thoracic, and lumbar spine, and can be inserted from behind(posteriorly) in the lumbar spine. This is of great importance in thatthe purpose of these devices is in the treatment of disc disease andprobably greater than 99 percent of all lumbar operations for thetreatment of disc disease are performed from being where the presentinvention can easily be utilized, but the BAGBY devices, as per hisdescription, cannot.

3. Disc Removal

The BAGBY invention requires the complete removal of the disc prior tothe drilling step, whereas the present invention eliminates thelaborious separate process of disc removal and efficiently removes thedisc and prepares the vertebral end plates in a single step.

4. Time Required

The present invention saves time over the BAGBY invention in that timeis not wasted laboring to remove the disc prior to initiating thefusion. Also, since with the present invention the procedure isperformed through a system of guarded instrumentation, time is notwasted constantly placing and replacing various soft tissue retractorsthroughout the procedure.

5. Implant Stability

Dislodgement of the implant would be a major source of device failure(an unsuccessful clinical result), and might result in patient paralysisor even death. As discussed, the BAGBY device lacks any specific meansof achieving stability and since it is pounded in against resistance toachieve vertebral distraction, it is susceptible to forcefuldislodgement by the tendency of the two distracted vertebrae, to returnto their original positions squeezing out the device. The presentinvention however is screwed into place. As there is no unscrewing forcepresent between the vertebrae and compression alone cannot dislodge theimplant, the implant is inherently stable by its design. Furthermore,the threads of the present invention are highly specialized in that theyare periodically interrupted such that the tall ends of each of the tabsso formed are blunted and twisted so as to resist accidental unscrewing.The removal of an implant with such “locking threads” requires the useof a special extractor included within the instrumentation. Thestability of the present invention is still further enhanced, again incontradistinction to the BAGBY device, by the presence of a “boneingrowth” surface texturing, which both increases the friction of thefit and allows for the direct growth of the vertebral bone into thecasing of the implant itself.

6. Spinal Stability

The present invention is not only self-stabilizing, it also providesstability to the adjacent vertebrae in at least three ways that theBAGBY device cannot. First, the BAGBY device is placed transverselyacross the joint in the center, leaving both vertebrae free to rock backand forth over this round barrel shaped axis, much like a board over abarrel, being used for a seesaw.

Secondly, as the BAGBY device lacks any specific design features toresist sliding, it may actually behave as a third body allowing thetranslation of the vertebrae relative to the device and to each other.

Thirdly, any device can only provide stability if it remains properlyseated. The present invention is inherently stable, and thereforeassures that it will stabilize the adjacent vertebrae; rather than, aswith the BAGBY device, where the instability of the spine to be treatedmay instead cause a dislocation of the implant, with further loss ofspinal stability.

7. The Collapse of the Interspace

While both the present invention and the BAGBY device can be fabricatedto withstand the compression forces within the interspace, theinterspace may nevertheless collapse under the superincumbent bodyweight as the implant settles into the vertebral bone. This is relatedto the load per unit area. Again the present invention is superior tothe BAGBY device in at least four ways. First, the present inventionoffers considerably greater surface area to distribute the load.Secondly, while the BAGBY device is placed centrally, the present deviceis placed bilaterally where the bone tends to be more cortical and muchstronger out towards the rim. Thirdly, the present invention supportsthe load achieving an “I” beam effect, whereas the BAGBY implant doesnot. Fourthly, it is not pressure alone that causes the collapse of thebone adjacent to the implant, but also bony erosion that is caused bythe motion under pressure of the implant against the bone. As discussedin item #6 above, the present invention alone is highly resistant tosuch motion, again diminishing the likelihood of erosion and interspacecollapse.

8. Bone Ingrowth Surface Texturing

The present invention has a surface treatment of known and conventionaltechnology to induce the growth of bone from the vertebrae directly intothe casing material of the implant itself. The BAGBY device has nosimilar feature.

9. Fusion Mass

The BAGBY invention calls for removing the disc and then drilling a holebetween the adjacent vertebrae. The bony debris so generated is then putinto the device. The present invention takes core of pure bone producingmarrow from the iliac crest, and then by use of a special press forciblyinjects the device with an extremely dense compressed core of thatosteogenic material until the material itself virtually extrudes fromevery cell of the implant.

10. The Probability of Achieving Fusion

The fusion rate within the spine is known to be related directly to theamount of exposed vascular bone bed area, the quality and quantity ofthe fusion mass available, and the extent of the stabilization obtainedwith all other factors being hold constant. It would be anticipated,that the fusion rate would be superior with the present invention ascompared to the BAGBY device, because of optimal implant stability (#5),optimal spinal stability (#6), bone ingrowth surface treatment (#8),superior fusion mass (#9), and the greater exposed vertebral bonysurface area (#7).

The last area of prior art possibly related to the present invention andtherefore, to be considered related to “BONY INGROWTH”, and patientseither describe methods of producing materials and or materials ordevices to achieve the same. Such patents would include:

U.S. Pat. No. 4,636,526 (DORMAN), U.S. Pat. No. 4,634,720 (DORMAN), U.S.Pat. No. 4,542,539 (ROWE), U.S. Pat. No. 4,405,319 (CONSENTINO), U.S.Pat. No. 4,439,152 (SMALL), U.S. Pat. No. 4,168,326 (BROEMER), U.S. Pat.No. 4,535,485 (ASHMAN), U.S. Pat. No. 3,987,499 (SCHARBACH), U.S. Pat.No. 3,605,123 (HAHN), U.S. Pat. No. 4,655,777 (DUNN), U.S. Pat. No.4,645,503 (LIN), U.S. Pat. No. 4,547,390 (ASHMAN), U.S. Pat. No.4,608,052 (VAN KAMPEN), U.S. Pat. No. 4,698,375 (DORMAN), U.S. Pat. No.4,661,536 (DORMAN), U.S. Pat. No. 3,952,334 (BOKROS), U.S. Pat. No.3,905,047 (LONG), U.S. Pat. No. 4,693,721 (DUCHEYNE), U.S. Pat. No.4,070,514 (ENTHERLY).

However, while the present invention would utilize bone ingrowthtechnology, it would do so with conventional technology.

In summary then, the present invention, instrumentation, and method,alone provides for a one stage discectomy, fusion, and interbodyinternal spinal fixation; that being performed more quickly, withgreater safety, and more affectively, for all of the aforementionedreasons than is possible with any other known art.

BRIEF SUMMARY OF THE INVENTION

The present invention comprises a series of artificial implants, thepurpose of which is to participate in, and directly cause bone fusionacross an intervertebral space following the excision of a damaged disc.Such implants are structurally load bearing devices, stronger than bone,capable of withstanding the substantial forces generated within thespinal interspace. Such devices have a plurality of macro sized cellsand openings, which can be loaded with fusion promoting materials, suchas autogenous bone, for the purpose of materially influencing theadjacent vertebrae to form a bony bond to the implants and to eachother. The implant casing may be surface textured or otherwise treatedby any of a number of known technologies to achieve a “bone ingrowthsurface” to further enhance the stability of the implant an to expeditethe fusion.

Further, said devices are so configured and designed so as to promotetheir own stability within the vertebral interspace and to resist beingdislodged, and furthermore, to stabilize the adjacent spinal segments.

The apparatus for preparing the vertebrae for insertion of the implantis also disclosed, such instrumentation and method allowing for therapid and safe removal of the disc, preparation of the vertebrae,performance of the fusion, and internal stabilization of the spinalsegment.

Discussion of the Instrumentation

The concept of performing various aspects of this surgery are notentirely new. Drills are frequently placed through hollow, tubularguards to protect the adjacent soft tissues. A set of instrumentsdeveloped by Ralph Cloward utilizes such a tubular drill guard on alarger scale, for the purpose of drilling into the cervical spine.However, this inventor is unaware of any set of instruments, system, orprocedure designed to allow the entire surgical procedure beyond theinitial exposure, to be performed blindly and with complete safetythrough a fixed sheath apparatus. Specific design features which combineto make this uniquely possible are as follows:

1. The availability of the specific implant.

2. The end of all the penetrating instrumentation is blunt faced.

3. All of the instruments have been stopped out at a predetermined depthto avoid overpenetration.

4. The design of the external sheath conforms to the spacial limitationsof the specific surgical site.

5. The design and use of a second or inner sheath allows for thedifference in size between the inside diameter of the outer sheath, andthe outside diameter of the drill itself. This difference beingnecessary to accommodate the sum of the distraction to be produced, andthe depth of the circumferential threading present on the implant.

6. A specially designed drill bit with a central shaft recess allows forthe safe collection of the drilling products, which can then be removedwithout disturbing the outer sheath by removing the drill bit and innersheath as a single unit.

7. A specially designed trephine for removing a core of bone slightlysmaller in diameter than the internal diameter of the implant cavityitself, however of a greater length.

8. A specially designed press for forcefully compressing and injectingthe long core of autogenous bone into the implant, such that it extrudesthrough the implant itself.

9. A specially designed driver extractor, which attaches to the implantand allows the implant to be either inserted or removed without itselfdissociating from the implant, except by the deliberate disengagement ofthe operator.

Objects of the Present Invention

It is an object of the present invention to provide an improved methodof performing a discectomy, a fusion, and an internal stabilization ofthe spine, and specifically, all three of the above simultaneously andas a single procedure.

It is another object of the present invention to provide an improvedmethod of performing a discectomy, a fusion, and an internalstabilization of the spine, which is both quicker and safer than ispossible by previous methods.

It is another object of the present invention to provide an improvedmethod of performing a discectomy, a fusion, and an internalstabilization of the spine, to provide for improved surgical spinalimplants.

It is another object of the present invention to provide an improvedmethod of performing a discectomy, a fusion, and an internalstabilization of the spine, which provides for an improved system ofsurgical instrumentation to facilitate the performance of the combineddiscectomy, fusion, and internal spinal stabilization.

These and other objects of the present invention will be apparent fromreview of the following specifications and the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is perspective view of the driver and sheath and its orientationto a vertebral structure.

FIG. 1A is a perspective view of the driver member for the outer sheath.

FIG. 2 is a perspective view of the outer sheath being inserted into thevertebrae structure.

FIG. 3 is a perspective view of the outer sheath and inner sheathassembly, with the drill bit of the present invention.

FIG. 3A is a side sectional view of the collar and drill bit of FIG. 3.

FIG. 4 is a perspective view of a cylindrical implant and vertebraestructure.

FIG. 4A is a perspective view of one preferred embodiment of theimplant.

FIG. 4B is a cross sectional view of the implant of FIG. 4A.

FIG. 4C is the driving and insertion equipment for the implant of FIG.4A.

FIG. 4d is a side sectional view of the driver and implant betweenvertebrae.

FIG. 5 is a sectional view of the vertebrae structure, taken along lines5—5 of FIG. 4.

DETAILED DESCRIPTION OF THE DRAWINGS

Preferred to FIG.1 a vertebrae structure comprising two vertebrae V anda disc D between the two vertebrae, is shown. A hollow tubular drillsleeve 10 has teeth 12 at its lower end. The sleeve 10 has an enlargeddiameter upper portion 14.

A driver 16, shown in FIG. 1A, consists of a solid tubular member 18 andan increased diameter head 20. The external diameter of the solidtubular member 18 is slightly smaller than the inside diameter of thehollow tubular drill sleeve 10 and has a length that is substantiallyshorter than the overall length of the hollow tubular drill sleeve 10.

The drill sleeve 10 is made of metal in order to be driven into thevertebrae V and be held in place by the teeth 12 of the drill sleeve 10.

Referring to FIG. 2 the drill sleeve 10 with the driver 16 installed isshown being driven into two vertebrae V on either side of a disc D byhammer H.

Referring to FIG.3 and 3a the drill assembly is shown. In FIG. 3 thedrill sleeve 10 is illustrated in the two vertebrae V, straddling thedisc D.

The retaining sleeve 15 has an outside diameter slightly smaller thanthe inside diameter of the drill sleeve 10, and a length substantiallythe same length as the drill sleeve 10. The retaining sleeve 15 has acollar 17 at its upper end for engaging the top of the drill sleeve 10.

The drill 22 comprises an upper portion 24, a central recessed portion26 and a lower cutting drill portion 28. The upper 24 and lower portion28 of the drill 22 have the same outside diameter. The drill 24 has acollar 30 attached to the upper portion 24 of the drill 22.

The outside diameter of the drill 22 is slightly smaller than the insidediameter of the retaining sleeve 15. The length of the drill, from thecollar 30 to the end of the drill bit, is such that a predeterminedportion of the drill bit 22 extends beyond the end 29 of the sleeve whenfully inserted.

Referring to FIG. 4, a cylindrical embodiment of the present inventionis shown, on implant positioned in the opening in the vertebrae and discformed by the drill 22, and a second implant shown prior toimplantation.

The cylindrical implant 50 comprises a hollow tubular member which inthe preferred embodiment is made of as ASTM surgically implantablematerial, and preferably Titanium. The cylindrical implant 50 is closedat one end 52 and open at the other end 54. The outer cylindricalimplant 50 has a series of macro-sized openings 56 though the side wallsof the cylindrical member 50. A series of external threads 53 are formedon the circumference of the cylindrical implant 50. The threads 53 arelocking threads having a series of interjections, the ends of which areblunted and twisted so as to resist unscrewing.

The open end 54 of the cylindrical implant 50 has an internal thread 51for receiving a complementary cap 52 which has an external thread 58 forengaging the internal threads 51 of the cylindrical member 50. The cap52 has a hexagonal opening 59 for use with an allen wrench fortightening the cap. A driver engaged element 70 is located on the rearsurface 60 of the implant. The driver engaged element 70 comprises araised rectangular portion 63 and a central threaded opening 65, forengaging the driver apparatus, shown in FIG. 4c and FIG. 4d. The drivingequipment 100 comprises a central tubular rod 102 having a threadfitting into opening 65 in the implant. An enlarged knurled knob 106 isaffixed to the other end of the rod 102 for ease in turning. The centralrod 102 is enclosed within a hollow tubular member 108, having a narrowlower portion 110 and an increased diameter upper portion 112. At theend of the lower portion 110 is a attachment member 114, having agenerally rectangular depression 116 for complementing the driverengaging element 70 of the implant 50. A pair of handles 118 and 120extend perpendicular from the upper position 112 of the tubular member108 to assist in turning the driver 100.

The operation is performed in the following manner: (Example LumbarSpine Posterior Approach) A skin incision is made directly over theinterspace to be operated on. The dissection is carried down along sideof the superspinous and intraspinous ligaments preserving thosestructures. A semi hemi laminotomy is performed at the upper level,removing sufficient bone to allow access into the interspace. Theligament flavum is removed and then the dural sac is protected byretracting it medially along with the traversing (inferior) nerve root.The superior nerve root or the root exiting beneath the pedicle at thelevel above is visualized and protected.

At this time the drill sleeve 10 is placed into the spinal canal withboth nerve roots directly inspected and protected. The drill sleeve 10is imbedded by teeth 12 spanning the disc space from the midline overand it is seated into the two vertebrae V across the disc D space byusing a driver 20. Once this is done, the driver 20 is removed and aretaining sleeve 15 is placed through the drill sleeve 10. Once seated,sleeve 10 provides absolute protection to the dural sac and nerve rootsas the remaining surgery is performed entirely through this sleeve.

The inner sleeve allows for the difference between the outside diameterof the drill 22 and the outside diameter of the threads 53 of thecylindrical implant 50. This then makes it possible to perform theentire operation through the an of the imbedded outer sleeve despite thedifference in diameter between the drill and the implant.

A drill 22 is then placed in the retaining sleeve 17. The drill 22 is ofsuch a length that it can not penetrate more then 28 millimeters beyondthe end of the drill sleeve 10. This, of course, could be varied andmade smaller for enhanced safety. However at the present time 27 to 28millimeters seems to be safe for probably 3 standard deviations of thepopulation. The drill 22 is attached to a power unit and the drillingtakes place.

The recessed central area between the reduced portion 26, allows for theaccumulation of the debris generated by the drilling. At this time,leaving the outer sleeve firmly embedded, the retaining sleeve 17 isremoved with the drill 22 as a single unit. All the vertebrae and discdebris that was generated during the drilling is contained within therecess and against the inside wall of the retaining sleeve 17 and cannot come out within the spinal canal. Once the retaining sleeve 17 anddrill 22 is out of the patient's operative field, all of the material sogenerated can be removed.

The next step is that a screw tap is put down through the drill sleeve10. The tap also has a collar on it that will automatically stop the tapfrom extending beyond 28 millimeters of penetration. The tap itself hasa blunt nose that would also avoid any perforation. The tap is thenremoved. The tap size has deliberately been selected so that it's innerroot diameter is 1.3 millimeters greater than the outside diameter ofthe drill 22. This insures that the interspace will be distracted by atleast that much once the implant is placed. The tap has its outsidediameter 1.2 millimeters greater than its root diameter. The tap isremoved and the space is now prepared to accept the cylindrical implant50.

The Implant 50 is prepared by utilizing the trephine, a hollow drill, toobtain a core of pure cancellous bone from the patients iliac crest ofslightly smaller diameter than the internal diameter of the implant butapproximately 6 mm longer. The implant 50 is place in a press likedevice like an ammo loader and the bone graft measuring approximately 32millimeters is then compressed into the hollow body of the implant (26mm) so that the bone graft fills the opening 54 and extends through theopenings 56. The cap 60 is then screwed on to the implant 50 by use ofan allen driver/wrench and the device is ready for implantation.

The inserter/remover is such that it locks onto the implant, so that theimplant can be moved either clockwise or counter-clockwise, screwed orunscrewed. The implant itself has for its root diameter the same exactroot diameter as the tap which is already noted is already 1.13millimeters greater than the drill and has an outside diameter, 1.5millimeters greater than its root. This is also 0.3 millimeters greaterthan the threads cut by the tap so that in inserting the device it isactually cutting through previously uncut bone helping to insure that itlocks in firmly. The threads on the implant 50 are locking threads sothat it is easier to screw the device in than for it to be unscrewed.However, with sufficient torque it is possible to extract the device ifones so desires.

Once the implant has been seated it is able to be inserted on 28millimeters. Since the implant 50 is only 26 millimeters in length, thisvirtually guarantees that the implant 50 will be recessed into thevertebral bodies more than 2 millimeters and can not protrude into thespinal canal.

Similarly, the implants shown in FIG. 4b can be implanted. The implantif FIG. 4b is a modified solid, having extensive channelling throughout,and has no cap. A central opening 61 permits insertion of the bone graftmaterial into the interior of the implant.

These implants have a surface configuration such as to induce boneingrowth through the implant, an into the wall of the vertebrae ineffect inducing fusion from one vertebrae in joint to the other, therebyeventually making the implant itself superfluous as the bone would dothe work.

The implant itself, because of its being made of stronger material thanbone, would provide structural support to the two vertebrae whileawaiting bone ingrowth. Once the bone ingrowth occurred, however, theimplant would be firmly and permanently fixed in place.

As shown in FIG. 4, more than one implant is inserted into the discspace, thereby preventing the rocking motion that would result in thedifficulties referred to above in the discussion of the Bagby patent.

While the invention has been described with regards to the preferredembodiment, it is recognized that alternative embodiment may be devisedwhich would not depart from the present invention.

What I claim is:
 1. An artificial interbody spinal fusion implant forinsertion across a disc space between two adjacent vertebral bodies of ahuman spine, said implant comprising: opposed arcuate portions adaptedfor placement toward and at least in part within the adjacent vertebralbodies and having a distance therebetween defining an implant heightgreater than the normal height of the disc space to be fused, each ofsaid opposed arcuate portions having at least one opening incommunication with one another for permitting the growth of bone fromvertebral body to adjacent vertebral body through said implant; aprotrusion extending from each of said opposed arcuate portions forengaging each of the adjacent vertebral bodies to maintain said implantwithin the disc space; and said implant comprising at least in part ofan implantation material other than bone.
 2. The spinal fusion implantof claim 1, wherein said protrusion comprises a thread.
 3. The spinalfusion implant of claim 1, wherein said protrusion comprises a ridge. 4.The spinal fusion implant of claim 1, wherein each of said opposedarcuate portions comprises an interior surface, said interior surfacesbeing spaced apart to define a hollow interior in communication withsaid at least one opening of each of said opposed arcuate portions. 5.The spinal fusion implant of claim 4, wherein said implant has a leadingend for insertion into the spine and an opposite trailing end, at leastone of said ends being open to allow access to said hollow interior. 6.The spinal fusion implant of claim 5, wherein said at least one endproviding access to said hollow interior of said implant is adapted tobe closed by a cap.
 7. The spinal fusion implant of claim 6, whereinsaid implant having said at least one end providing access to saidhollow interior is in combination with a cap adapted to close saidhollow interior.
 8. The spinal fusion implant of claim 1, furthercomprising a plurality of cells for retaining fusion promotingsubstance.
 9. The spinal fusion implant of claim 1, wherein said opposedarcuate portions have a porous surface.
 10. The spinal fusion implant ofclaim 1, wherein said implantation material is porous.
 11. The spinalfusion implant of claim 1, wherein said implantation material comprisesan ASTM material suitable for use as a spinal fusion implant.
 12. Thespinal fusion implant of claim 1, wherein said implantation materialcomprises titanium.
 13. The spinal fusion implant of claim 1, whereinsaid implantation material comprises a fusion promoting substance otherthan bone.
 14. The spinal fusion implant of claim 1, wherein saidimplantation material comprises a bone ingrowth material.
 15. The spinalfusion implant of claim 1, wherein said implantation materialintrinsically participates in the growth of bone from one of theadjacent vertebral bodies to the other of the adjacent vertebral bodies.16. The spinal fusion implant of claim 1, wherein said implant istreated with a fusion promoting substance.
 17. The spinal fusion implantof claim 1, wherein said opposed arcuate portions have a bone ingrowthsurface.
 18. The spinal fusion implant of claim 1, wherein saidimplantation material is stronger than bone.
 19. The spinal fusionimplant of claim 1, in combination with a source of osteogenesis. 20.The spinal fusion implant of claim 1, in combination with a bone growthpromoting substance.
 21. The spinal fusion implant of claim 20, incombination with bone.
 22. The spinal fusion implant of claim 21,wherein said bone is compressively loaded in said implant.
 23. Thespinal fusion implant of claim 20, in combination with a material otherthan bone.
 24. The spinal fusion implant of claim 20, in combinationwith a hydroxyapatite.
 25. The spinal fusion implant of claim 1, incombination with a guard and a bone removal device, said guard forproviding protected access to prepare across the spinal disc and intothe adjacent vertebral bodies the implantation space, said guard havinga passage through which said bone removal device passes to form theimplantation space through said guard.
 26. The spinal fusion implant ofclaim 25, wherein said implant is configured to have a height greaterthan the height of the implantation space and to pass through saidpassage of said guard.
 27. The spinal fusion implant of claim 1, whereinsaid implant has a leading end for insertion into the spine and anopposite trailing end, said trailing end being adapted to cooperativelyengage and insertion device for inserting said implant into the spine.28. The spinal fusion implant of claim 27, in combination with aninsertion device for inserting said implant into the spine, saidinsertion device being adapted to cooperatively engage said trailing endof said implant.
 29. An artificial interbody spinal fusion implant forinsertion across a disc space between two adjacent vertebral bodies of ahuman spine, said implant comprising a material other than bone for usein combination with a fusion promoting substance other than bone, saidimplant having opposed portions adapted for placement toward theadjacent vertebral bodies and having a distance therebetween defining animplant height greater than normal height of the disc space to be fused,and said opposed portions having at least one passage passingtherethrough for permitting the growth of bone from vertebral body toadjacent vertebral body through said passage.
 30. The spinal fusionimplant of claim 29, further comprising a protrusion extending from eachof said opposed portions for engaging each of the adjacent vertebralbodies to maintain said implant within the disc space.
 31. The spinalfusion implant of claim 30, wherein said protrusion comprises a thread.32. The spinal fusion implant of claim 30, wherein said protrusioncomprises a ridge.
 33. The spinal fusion implant of claim 20, whereinsaid opposed portions are arcuate.
 34. The spinal fusion implant ofclaim 29, wherein each of said opposed portions comprise an interiorsurface, said interior surfaces being spaced apart to define a hollowinterior in communication with said at least one opening of each of saidopposed arcuate portions.
 35. The spinal fusion implant of claim 34,wherein said implant has a leading end for insertion into the spine andan opposite trailing end, at least one of said ends being open to allowaccess to said hollow interior.
 36. The spinal fusion of claim 35,wherein said at least one end providing access to said hollow interiorof said implant is adapted to be closed by a cap.
 37. The spinal fusionimplant of claim 36, wherein said implant having said at least one endproviding access to said hollow interior is in combination with a capadapted to close said hollow interior.
 38. The spinal fusion implant ofclaim 29, further comprising a plurality of cells for retaining a fusionpromoting substance.
 39. The spinal fusion implant of claim 29, whereinsaid opposed portions have a porous surface.
 40. The spinal fusion ofclaim 29, wherein said implant material is porous.
 41. The spinal fusionimplant of claim 29, wherein said opposed portions have a bone ingrowthsurface.
 42. The spinal fusion implant of claim 29, wherein said implantmaterial intrinsically participates in the growth of bone from one ofthe adjacent vertebral bodies to the other of the adjacent vertebralbodies.
 43. The spinal fusion implant of claim 29, wherein said implantmaterial is stronger than bone.
 44. The spinal fusion implant of claim29, in combination with a source of osteogenesis.
 45. The spinal fusionimplant of claim 29, in combination with a bone growth promotingsubstance.
 46. The spinal fusion implant of claim 45, in combinationwith bone.
 47. The spinal fusion implant of claim 46, wherein said boneis compressively loaded in said implant.
 48. The spinal fusion implantof claim 45, in combination with a material other than bone.
 49. Thespinal fusion implant of claim 45, in combination with a hydroxyapatite.50. The spinal fusion implant of claim 29, in combination with a guardand a bone removal device, said guard for providing protected access toprepare across the spinal disc and into the adjacent vertebral bodiesthe implantation space, said guard having a passage through which saidbone removal device passes to form the implantation space through saidguard.
 51. The spinal fusion implant of claim 50, wherein said implantis configured to have a height greater than the height of theimplantation space and to pass through said passage of said guard. 52.The spinal fusion implant of claim 29, wherein said implant has aleading end for insertion into the spine and an opposite trailing end,said trailing end being adapted to cooperatively engage an insertiondevice for inserting said implant into the spine.
 53. The spinal fusionimplant of claim 52, in combination with an insertion device forinserting said plant into the spine, said insertion device being adaptedto cooperatively engage said trailing end of said implant.
 54. Anartificial interbody spinal fusion implant for insertion across a discspace between two adjacent vertebral bodies of a human spine, saidimplant comprising: opposed portions adapted for placement toward theadjacent vertebral bodies and having a distance therebetween defining animplant height greater than the normal height of the disc space to befused, said opposed portions having a plurality of openings passingtherethrough for permitting the growth of bone through said implant fromvertebral body to adjacent vertebral body; a protrusion extending fromeach of said opposed portions for engaging the adjacent vertebral bodiesto maintain said implant within the disc space and between the adjacentvertebral bodies; and said implant comprising at least in part of asuitable implantation material other than bone.
 55. The spinal fusionimplant of claim 54, wherein said protrusion comprises a thread.
 56. Thespinal fusion implant of claim 54, wherein said protrusion comprises aridge.
 57. The spinal fusion implant of claim 54, wherein said opposedportions are arcuate.
 58. The spinal fusion implant of claim 54, furthercomprising extensive channeling throughout said implant.
 59. The spinalfusion implant of claim 54, wherein each of said opposed portionscomprises an interior surface, said interior surface being spaced apartto define a hollow interior in communication with said plurality ofopenings of said opposed portions.
 60. The spinal fusion implant ofclaim 59, wherein said implant has a leading end for insertion into thespine and an opposite trailing end, at least one of said ends being opento allow access to said hollow interior.
 61. The spinal fusion implantof claim 60, wherein said at least one end providing access to saidhollow interior of said implant is adapted to be closed by a cap. 62.The spinal fusion implant of claim 61, wherein said implant having saidat least one end providing access to said hollow interior is incombination with a cap adapted to close said hollow interior.
 63. Thespinal fusion implant of claim 54, further comprising a plurality ofcells for retaining a fusion promoting substance.
 64. The spinal fusionimplant of claim 54, wherein said opposed portions are porous.
 65. Thespinal fusion implant of claim 54, wherein said implantation material isporous.
 66. The spinal fusion implant of claim 54, wherein saidimplantation material comprises an ASTM material suitable for use as aspinal fusion implant.
 67. The spinal fusion implant of claim 54,wherein said implantation material comprises titanium.
 68. The spinalfusion implant of claim 54, wherein said implantation material comprisesa fusion promoting substance.
 69. The spinal fusion implant of claim 54,wherein said implantation material comprises a bone ingrowth material.70. The spinal fusion implant of claim 54, wherein said materialintrinsically participates in the growth of bone from one of theadjacent vertebral bodies.
 71. The spinal fusion implant of claim 54,wherein said implant is treated with a fusion promoting substance. 72.The spinal fusion implant of claim 54, wherein said implantationmaterial is stronger than bone.
 73. The spinal fusion implant of claim54, in combination with a source of osteogenesis.
 74. The spinal fusionimplant of claim 54, in combination with a bone growth promotingsubstance.
 75. The spinal fusion implant of claim 74, in combinationwith bone.
 76. The spinal fusion implant of claim 75, wherein said boneis compressively loaded in said implant.
 77. The spinal fusion implantof claim 74, in combination with a material other than bone.
 78. Thespinal fusion implant of claim 74, in combination with a hydroxyapatite.79. The spinal fusion implant of claim 54, in combination with a guardand a bone removal device, said guard for providing protected access toprepare across the spinal disc and into the adjacent vertebral bodiesthe implantation space, said guard having a passage through which saidbone removal device passes to form the implantation space through saidguard.
 80. The spinal fusion implant of claim 79, wherein said implantis configured to have a height greater than the height of theimplantation space and to pass through said passage of said guard. 81.The spinal fusion implant of claim 54, wherein said implant has aleading end for insertion into the spine and an opposite trailing end,said trailing end being adapted to cooperatively engage an inerstiondevice for inserting said implant into the spine.
 82. The spinal fusionimplant of claim 81, wherein said implant has a leading end forinerstion into the spine, said insertion device being adapted tocooperatively engage said trailing end of said implant.
 83. Anartificial interbody spinal fusion implant for insertion across a discspace between two adjacent vertebral bodies of a human spine, saidimplant comprising: opposed arcuate portions adapted for placementtoward and at least in part within the adjacent vertebral bodies andhaving a distance therebetween defining an implant height greater thanthe normal height of the disc space to be fused, each of said opposedarcuate portions having at least one opening communicating with oneanother for permitting the growth of bone from vertebral body toadjacent vertebral body through said implant; a thread portion formed onthe exterior of each of said opposed arcuate portions for engaging theadjacent vertebral bodies to maintain said implant within the discspace; and said implant comprising at least in part of a suitableimplantation material other than bone.
 84. The spinal fusion implant ofclaim 83, wherein said thread portion is an interrupted thread.
 85. Thespinal fusion implant of claim 83, wherein said thread portion on eachof said arcuate portions form a single helix.
 86. The spinal fusionimplant of claim 83, wherein each of said opposed arcuate portionscomprises an interior surface, said interior surfaces being spaced apartto define a hollow interior in communication with said at least oneopening of each of said opposed arcuate portions.
 87. The spinal fusionimplant of claim 83, in combination with a fusion promoting substancewithin said hollow interior.
 88. The spinal fusion implant of claim 86,said implant having a leading end for insertion into the spine and anopposite trailing end, at least one of said ends being open to allowaccess to said hollow interior.
 89. The spinal fusion implant of claim88, wherein said at least one end providing access to said hollowinterior of said implant is adapted to be closed by a cap.
 90. Thespinal fusion implant of claim 89, wherein said implant having said atleast one end providing access to said hollow interior is in combinationwith a cap adapted to close said hollow interior.
 91. The spinal fusionimplant of claim 83, further comprising a plurality of cells forretaining fusion promoting substance.
 92. The spinal fusion implant ofclaim 83, wherein said opposed arcuate portions have a porous surface.93. The spinal fusion implant of claim 83, wherein said implantationmaterial is porous.
 94. The spinal fusion implant of claim 83, whereinsaid implantation material comprises an ASTM material suitable for useas a spinal fusion implant.
 95. The spinal fusion implant of claim 83,wherein said implantation material comprises titanium.
 96. The spinalfusion implant of claim 83, wherein said implantation material comprisesa fusion promoting substance other than bone.
 97. The spinal fusionimplant of claim 83, wherein said implantation material comprises a boneingrowth material.
 98. The spinal fusion implant of claim 83, whereinsaid implantation material intrinsically participates in the growth ofbone from one of the adjacent vertebral bodies to the other of theadjacent vertebral bodies.
 99. The spinal fusion implant of claim 83,wherein said implant is treated with a fusion promoting substance. 100.The spinal fusion implant of claim 83, wherein said opposed arcuateportions have a bone ingrowth surface.
 101. The spinal fusion implant ofclaim 83, wherein said implantation material is stronger than bone. 102.The spinal fusion implant of claim 83, in combination with a source ofosteogenesis.
 103. The spinal fusion implant of claim 83, in combinationwith a bone growth promoting substance.
 104. The spinal fusion implantof claim 103, in combination with bone.
 105. The spinal fusion implantof claim 104, wherein said bone is compressively loaded in said implant.106. The spinal fusion implant of claim 103, in combination with amaterial other than bone.
 107. The spinal fusion implant of claim 103,in combination with hydroxyapatite.
 108. The spinal fusion implant ofclaim 83, in combination with a guard and a bone removal device, saidguard for providing protected access to prepare across the spinal discand into the adjacent vertebral bodies the implantation space, saidguard having a passage through which said bone removal device passes toform the implantation space through said guard.
 109. The spinal fusionimplant of claim 108, wherein said implant is configured to have aheight greater than the height of the implantation space and to passthrough said passage of said guard.
 110. The spinal fusion implant ofclaim 82, wherein said implant has a leading end for insertion into thespine and an opposite trailing end, said trailing end being adapted tocooperatively engage an insertion device for inserting said implant intothe spine.
 111. The spinal fusion implant of claim 110, in combinationwith an insertion device for inserting said implant into the spine, saidinsertion device being adapted to cooperatively engage said trailing endof said iomplant.
 112. An artificial interbody spinal fusion implant forinsertion across a disc space between two adjacent vertebral bodies of ahuman spine, said implant comprising: opposed portions adapted forplacement toward and the adjacent vertebral bodies and having a distancetherebetween defining an implant height greater than the normal heightof the restored disc space to be fused, said opposed portions eachhaving at least one opening passing therethrough for permitting thegrowth of bone through said implant from vertebral body to adjacentvertebral body; a thread made of a surgically implantable metalextending from each of said opposed portions for engaging the adjacentvertebral bodies to maintain said implant within the disc space andbetween the adjacent vertebral bodies; and said implant comprising atleast in part of a suitable implantation material other than bone. 113.The spinal fusion implant of claim 112, wherein each of said opposedportions comprises an interior surface, said interior surfaces beingspaced apart to define a hollow interior in communication with said atleast one opening of each of said opposed portions.
 114. The spinalfusion implant of claim 113, in combination with a fusion promotingsubstance within said hollow interior.
 115. The spinal fusion implant ofclaim 113, said implant having a leading end for insertion into thespine and an opposite trailing end, at least one of said ends being opento allow access to said hollow interior.
 116. The spinal fusion implantof claim 115, wherein said at least one end providing access to saidhollow interior of said implant is adapted to be closed by a cap. 117.The spinal fusion implant of claim 116, wherein said implant having saidat least one end providing access to said hollow interior is incombination with a cap adapted to close said hollow interior.
 118. Thespinal fusion implant of claim 112, further comprising a plurality ofcells for retaining fusion promoting substance.
 119. The spinal fusionimplant of claim 112, wherein said opposed portions have a poroussurface.
 120. The spinal fusion implant of claim 112, wherein saidimplantation material is porous.
 121. The spinal fusion implant of claim112, wherein said implantation material comprises an ASTM materialsuitable for use as a spinal fusion implant.
 122. The spinal fusionimplant of claim 112, wherein said implantation material comprisestitanium.
 123. The spinal fusion implant of claim 112, wherein saidimplantation material comprises a fusion promoting substance other thanbone.
 124. The spinal fusion implant of claim 112, wherein saidimplantation material comprises a bone ingrowth material.
 125. Thespinal fusion implant of claim 112, wherein said implantation materialintrinsically participates in the growth of bone from one of theadjacent vertebral bodies to the other of the adjacent vertebral bodies.126. The spinal fusion implant of claim 112, wherein said implant istreated with a fusion promoting substance.
 127. The spinal fusionimplant of claim 112, wherein said opposed portions have a bone ingrowthsurface.
 128. The spinal fusion implant of claim 112, wherein saidimplantation material is stronger than bone.
 129. The spinal fusionimplant of claim 112, in combination with a source of osteogenesis. 130.The spinal fusion implant of claim 112, in combination with a bonegrowth promoting substance.
 131. The spinal fusion implant of claim 116,in combination with bone.
 132. The spinal fusion implant of claim 117,wherein said bone is compressively loaded in said implant.
 133. Thespinal fusion implant of claim 130, in combination with a material otherthan bone.
 134. The spinal fusion implant of claim 130, in combinationwith hydroxyapatite.
 135. The spinal fusion implant of claim 112, incombination with a guard and a bone removal device, said guard forproviding protected access to prepare across the spinal disc and intothe adjacent vertebral bodies the implantation space, said guard havinga passage through which said bone removal device passes to form theimplantation space through said guard.
 136. The spinal fusion implant ofclaim 135, wherein said implant is configured to have a height greaterthan the height of the implantation space and to pass through saidpassage of said guard.
 137. The spinal fusion implant of claim 112,wherein said implant has a leading end for insertion into the spine andan opposite trailing end, said trailing end being adapted tocooperatively engage an insertion device for inserting said implant intothe spine.
 138. The spinal fusion implant of claim 137, in combinationwith a insertion device for inserting said implant into said spine, saidinsertion device being adapted to cooperatively engage said trailing endof said implant.
 139. An artificial interbody spinal fusion implant forinsertion across a disc space between two adjacent vertebral bodies of ahuman spine, said implant comprising: opposed arcuate portions adaptedfor placement toward and at least in part within the adjacent vertebralbodies and having a distance therebetween defining an implant heightgreater than the normal height of the disc space to be fused, each ofsaid opposed arcuate portions having at least one opening communicatingwith one another for permitting the growth of bone from vertebral bodyto adjacent vertebral body through said implant; a series of surfaceprojections formed on the exterior of each of said opposed arcuateportions for penetrably engaging the adjacent vertebral bodies tomaintain said implant within the disc space; and said implant comprisingat least in part of a suitable implantation material other than bone.140. The spinal fusion implant of claim 139, wherein each of said seriesof surface projections comprises a ridge.
 141. The spinal fusion implantof claim 139, wherein each of said opposed arcuate portions comprises aninterior surface, said interior surfaces being spaced apart to define ahollow interior in communication with said at least one opening of eachof said opposed arcuate portions.
 142. The spinal fusion implant ofclaim 141, in combination with a fusion promoting substances within saidhollow interior.
 143. The spinal fusion implant of claim 141, saidimplant having a leading end for insertion into the spine and anopposite trailing end, at least one of said ends being open to allowaccess to said hollow interior.
 144. The spinal fusion implant of claim143, wherein said at least one end providing access to said hollowinterior of said implant is adapted to be closed by a cap.
 145. Thespinal fusion implant of claim 144, wherein said implant having said atleast one end providing access to said hollow interior is in combinationwith a cap adapted to close said hollow interior.
 146. The spinal fusionimplant of claim 139, further comprising a plurality of cells forretaining fusion promoting substance.
 147. The spinal fusion implant ofclaim 139, wherein said opposed arcuate portions have a porous surface.148. The spinal fusion implant of claim 139, wherein said implantationmaterial is porous.
 149. The spinal fusion implant of claim 139, whereinsaid implantation material comprises an ASTM material suitable for useas a spinal fusion implant.
 150. The spinal fusion implant of claim 139,wherein said implantation material comprises titanium.
 151. The spinalfusion implant of claim 139, wherein said implantation materialcomprises a fusion promoting substance other than bone.
 152. The spinalfusion implant of claim 139, wherein said implantation materialcomprises bone ingrowth material.
 153. The spinal fusion implant ofclaim 139, wherein said implantation material intrinsically participatesin the growth of bone from one of the adjacent vertebral bodies to theother of the adjacent vertebral bodies.
 154. The spinal fusion implantof claim 139, wherein said implant is treated with a fusion promotingsubstance.
 155. The spinal fusion implant of claim 139, wherein saidopposed arcuate portions have a bone ingrowth surface.
 156. The spinalfusion implant of claim 139, wherein said implant material is strongerthan bone.
 157. The spinal fusion implant of claim 139, in combinationwith a source of osteogenesis.
 158. The spinal fusion implant of claim139, in combination with a bone growth promoting substance.
 159. Thespinal fusion implant of claim 158, in combination with bone.
 160. Thespinal fusion implant of claim 139, wherein said bone is compressivelyloaded in said implant.
 161. The spinal fusion implant of claim 158, incombination with a material other than bone.
 162. The spinal fusionimplant of claim 158, in combination with hydroxyapatite.
 163. Thespinal fusion implant of claim 139, in combination with a guard and abone removal device, said guard for providing protected access toprepare across the spinal disc and into the adjacent vertebral bodiesthe implantation space, said guard having a passage through which saidbone removal device passes to form the implantation space through saidguard.
 164. The spinal fusion implant of claim 163, wherein said implantis configured to have a height greater than the height of theimplantation space and to pass through said passage of said guard. 165.The spinal fusion implant of claim 139, wherein said implant has aleading end for insertion into the spine and an oppoiste trailing end,said trailing end being adapted to cooperatively engage an insertiondevice for inserting siad implant into the spine.
 166. The spinal fusionimplant of claim 165, in combination with an insertion device forinserting said implant into the spine, said insertion device beingadapted to cooperatively engge said trailing end of said implant.